Clean up the naming of PCI python modules

Something that has been bothering me when looking at the PCI code is
that the modules in /nova/pci/ unnecessarily were prefixed with pci_.
For instance, nova/pci/pci_device.py, whereas all other module directory
organizations for all other code in Nova uses the directory name to
demarcate a submodule.

This patch simply gets the nova/pci/ modules in-line with the standard
set everywhere else in Nova and cuts off the pci_ prefix from the module
names.

Change-Id: Ia5ca13f674f15b41e22b8488efe44eb926e5e4eb
Merge "Clean up the naming of PCI python modules"